Conventionally, an epoxy resin is used for encapsulating because of its good molding, adhesion, mechanical and moisture resistant properties. Recently, as consumers prefer smaller, lighter and more sophisticated electronic devices, more integrated semiconductor devices are required and requirements for an epoxy resin used for encapsulating the devices are getting severer.
As an IC or LSI package, high-density packages such as Lead on Chip (LOC) type TSOP, Ball Grid Array, and QFN are predominantly used. A problem with these packages is a warpage after encapsulation due to imbalanced resin thickness between the upper and lower sides of the package or a one-side encapsulation. One method to prevent the warpage is to increase a degree of cross linkage and a glass transition temperature of an encapsulating resin. However, this causes an increase in modulus of elasticity of a cured product. Further, a higher reflow temperature of Pb-free solder causes increase in susceptibility to moisture, so that a problem of peeling at an interface between a cured product of an epoxy resin and a substrate, or between a semiconductor device and an encapsulating epoxy resin occurs. To suppress moisture absorption, larger amount of inorganic filler may be incorporated in a composition. However, a composition containing such a larger amount of filler has an increased viscosity to cause problems in molding such as defects in a cured product and wire sweep. To decrease viscosity and to improve reflow resistance, use is made of a resin having low melt viscosity. However, due to a low glass transition temperature, impurity ions in the composition tend to migrate when exposed to a high temperature for a long time, resulting in low reliability of a semiconductor package.
Japanese Patent No. 3137202 discloses an epoxy resin composition comprising 1,1-bis(2,7-diglycidyloxy-1-naphthyl)alkane. A cured product of the composition is heat and moisture resistant, and overcomes problems of hardness and brittleness of a cured product of a conventional heat resistant epoxy resin.
Japanese Patent Application Laid-Open No. 2005-15689 discloses an epoxy resin composition comprising (A) epoxy resin mixture and (B) a curing agent, wherein the epoxy resin mixture (A) comprising 1,1-bis(2,7-diglycidyloxy-1-naphthyl)alkane (a1) 1-(2,7-diglycidyloxy-1-naphthyl)-1-(2-glycidyloxy-1-naphthyl)alkane (a2), and 1,1-bis(2-glycidyloxy-1-naphthyl)alkane (a3) in an amount of 40 to 95 parts by weight per total 100 parts by weight of components (a1), (a2) and (a3), and (B) a curing agent.
Japanese Patent No. 3451104, 3537859, and 3551281 disclose an epoxy resin composition comprising the epoxy resin represented by the following formula (1).

It was found that the composition tend to cause a semiconductor device to warp when it is encapsulated by the composition.